In a typical fiber optic cable, bundles of optical fibers are surrounded by a number of protective layers, with the fiber bundles being encased within a core tube which is then surrounded by a thin layer of armor, which is usually about 5 or 6 mils thick. The core tube is most often formed from a relative soft material, such as polypropylene, and the armor is usually formed from a relative hard material, such as a metal. The outermost layer of the fiber optic cable is a jacket designed to provide protection against the environment within which the fibers are placed. Layers of water blocking material may be formed around both the core tube and the armor within the jacket.
For an installer or lineman to gain access to the fiber bundles, in order, for example, to perform a splicing operation, the various protective layers must be removed in a manner which does not harm the optical fibers within the fiber bundles, thus the removal of the armor from the core tube is a rather delicate procedure which must be accomplished without damaging the core tube or the fiber bundles.
A common approach in the industry for the removal of the armor is to manufacture the fiber optic cables with a rip cord formed from a high tensile strength yarn, such as Kevlar.RTM. manufactured by E. I. Du Pont de Nemours and Company. The rip cord is placed between the core tube and the layer of armor opposite a location where ends of the armor circumferentially overlap. To expose the core tube, the armor is cut along the axis of the cable in order to draw a working length of the rip cord. Due to the strength of the rip cord and the thin layer of armor, the rip cord cuts through the layer of armor when the rip cord is pulled in a direction substantially transverse to the axis of the cable. Once the armor has been cut, the armor is separated along the cut to expose the core tube.
The use of a rip cord, however, is not the most reliable or safest approach. The rip cord frequently breaks when it is pulled in the direction transverse to the axis of the cable. One reason for these frequent breaks is that even though the rip cord is a high strength material, the edges of the armor may be sharp enough to sever the rip cord. When the rip cord is pulled, the unexposed portion of the fiber optic cable is pulled at an angle relative to the exposed portion of the fiber optic cable which results in a bending or kinking thereof. This bend or kink in the cable can and often does cause damage to the optical fibers. The smaller fiber optic cables bend more easily and are therefore more prone to this type of damage. There is therefore a need in the industry for a reliable way to expose the core tube which does not cause any damage or at least minimizes damage to the optical fibers.
The use of a rip cord in cutting or separating the armor is also a rather time consuming process and thus economically undesirable. Before the rip cord can be pulled, the armor must first be cut, as by pliers or side cutters, along the axis of the cable to expose enough of the rip cord so that it may be grasped by hand. With a working length of the rip cord exposed, the rip cord can then be pulled in the direction transverse to the axis of the cable to expose the core tube. If the rip cord breaks, which is fairly common, the armor must again be cut to expose another working length of the rip cord. After the desired length of armor has been cut, the armor must then be separated along the cut to expose the core tube. Thus the steps involved in using a rip cord can consume a relatively large amount of time. A need therefore exists for a quick and efficient process to expose the core tube.
In comparison to a splice performed at an end of the fiber optic cable, the use of a rip cord to prepare the cable for a mid-sheath splice is even more complicated. The mid-sheath splice requires an installer or lineman to cut the armor from the center of the cable, which is much more difficult than from the ends of the cable. Because of this difficulty, the mid-sheath splice presents a larger risk that the core tube and, consequently, the fibers will become damaged during the cutting of the armor. In all, the rip cord is harder to access and the core tube is more likely to become damaged with a mid-sheath splice than with a splice performed at an end of the cable.
Some of the smaller fiber optic cables, such as the MINI-LXE, are not manufactured with a rip cord. For these smaller fiber optic cables and others that do not have a rip cord, the process of exposing the core tube is even more difficult since the entire length of the armor must be cut by hand. The use of a pair of pliers or side cutters is a much more time consuming process than the process of exposing the core tube by means of a rip cord. The use of pliers or side cutters also presents a larger risk that the core tube will become damaged. Consequently, a need exists in the industry for a quick and safe manner of exposing the core tube in fiber optic cables which are formed without rip cords.